KANDAHAR, Afghanistan (AFP) – A Taliban cell behind a wave of attacks which killed four people in one of Afghanistan's biggest cities looked close to destruction Sunday after holding out for over 24 hours.

Two attackers who were holed up in a building near Kandahar's intelligence headquarters have been killed, leaving just one more inside, provincial spokesman Zalmay Ayoubi said.

The breakthrough came after heavily-armed militants breached security in a sweeping assault which wounded nearly 50 people across the city, the birthplace and strategic heart of the Taliban.

The attacks are the most significant since the Taliban announced the start of their annual spring offensive last week and vowed to step up their fight after US commandos killed Osama bin Laden in neighbouring Pakistan.

The dramatic standoff began at around 1:00 pm (0830 GMT) Saturday when a squad of Taliban armed with guns and rocket-propelled grenades attacked the governor's office from nearby buildings.

Officials said at least 10 blasts, including seven suicide attacks, rocked the city as assaults spread to other sites including police stations and the office of the National Directorate of Security (NDS).

Although the violence died down overnight, several Taliban fighters still occupied a traffic police building on Sunday, armed with guns, rockets and grenades.

It is thought they may also have been equipped with suicide vests. Two have now been killed but a third remains in the building, according to Ayoubi.

"Two attackers were shot dead. There is one person still in there," he said.

"Eight vehicles packed with explosives were found today and destroyed by foreign forces. One suicide bomber driving a car was identified, shot at and killed by Afghan security forces."

Provincial officials say that 20 insurgents have now been killed and at least seven captured.

Kandahar's streets were virtually deserted and the city was relatively quiet on Sunday with occasional gunfire, an AFP reporter said, while roads into the city have been blocked off.

A doctor at Kandahar's main hospital, Mohammad Hashim, said that two civilians and two members of the Afghan security forces had been killed.

"We have registered a total of 46 wounded so far. Twenty-four of the wounded are security personnel and the rest are civilians," he said. "We have also registered four dead -- two civilians and two security personnel."

Afghan President Hamid Karzai has branded the attack "revenge" for this week's killing of the Al-Qaeda leader by US forces in Pakistan. The Taliban, however, said the operation was planned several weeks in advance.

A spokesman for the NATO-led International Security Assistance Force (ISAF) whose troops were involved in the operation, Major General James Laster, described it as a "spring offensive spectacular attack which was thwarted".

There are around 130,000 foreign troops in Afghanistan. Limited withdrawals from seven relatively peaceful areas are due to start in July ahead of the planned end of foreign combat operations in 2014.

Control of Kandahar, in the heart of the restive south, is seen as key to US-led efforts to end the nearly 10-year Taliban insurgency and hand Afghan forces responsibility for national security in three years.

International forces say that the city and its surrounding area, traditionally hotbeds of unrest, are now safer following months of intense fighting last year to clear Taliban strongholds.

But government officials and institutions are still frequently targeted by militants in the city.

Nearly 500 Taliban prisoners escaped from Kandahar's prison last month through a huge tunnel. Also in April, Kandahar's police chief was killed by an attacker in a police uniform, while Wesa's deputy was assassinated in January.